Commodity polymers are typically produced from petrochemical sources by well-known synthetic means. However, recent advances in technology have resulted in the promise of new sources of commodity polymers. Particularly promising is the production of plastic resins using living organisms (“bioplastic” or Biopol), including bacteria to produce polymers such as polyhydroxyalkanoate (PHA); a number of bacteria which naturally produce PHA are also promising sources of PHA. (see for example, NOVEL BIODEGRADABLE MICROBIAL POLYMERS, E. A. Dawes, ed., NATO ASI Series, Series E: Applied Sciences—Vol. 186, Kluwer Academic Publishers (1990); Poirier, Y., D. E. Dennis, K. Klomparens and C. Somerville, “Polyhydroxybutyrate, a biodegradable thermoplastic produced in transgenic plants”, SCIENCE, Vol. 256, pp. 520-523 (1992). In a large scale production, for example agricultural production, isolation and culture of a new organism and cheap raw material for the production of bioplastic is a critical step for determining the practical feasibility of such technology.
PHB is an energy storage material produced by a variety of bacteria in response to environmental stress and is a homopolymer of D-(−)-3-hydroxybutyrate of the formula 1 which has properties comparable to polypropylene. Because PHB is biodegradable, there is considerable interest in using PHB for packaging purposes as opposed to other plastic materials in order to reduce the environmental impact of human garbage. PHB also has utility in antibiotics, drug delivery, medical suture and bone replacement applications. PHB is commercially produced from Alcaligenes eutrophus and sold under the trade name Biopol.
As described above and by Slater et al, in “Cloning and Expression in Escherichia coli of the Alcaligenes entrophus H16 Poly-beta-Hydroxybutyrate Biosynthetic Pathway”, Journal of Bacteriology, Vol. 170, No. 10, October, 1988, p. 4431-4436, which is also incorporated herein by reference, it was shown that E. coli could be genetically transformed with genes from A. eutrophus which code for the PHB biosynthetic pathway. E. coli are a far better vehicle for producing PHB than A. eutrophus since more is known about handling the bacteria, E. coli, i.e. E coli is more easily controlled and manipulated. The transformed E. coli is able to express PHB in relatively large quantities.
Despite PHB's advantages over other materials, its high cost of production has hindered its performance in the market. Currently, PHB is produced in transformed E. coli by growing the E. coli on luria broth (LB) and using glucose as the carbon source.
Approximately one third of the production cost of PHB is attributable to the rich LB medium and the glucose. If a less expensive carbon source could be utilized, the overall cost of PHB production could be significantly reduced. In addition, much of the total cost of PHB production is attributable to purifying the PHB produced in the E. coli. Currently, PHB is purified by centrifugation, followed by mechanical lysis of the cells to release PHB, a high temperature procedure to agglomerate the PHB, and finally a spray drying step to procure to agglomerate the PHB, and finally a spray drying step to procure the purified granules. If a less expensive method were available for collecting the PHB from a new organism of high efficiency together with the application of a cheap carbon source, the overall cost of PHB production could be significantly reduced.
In view of the above, there is a need for a simple and economical process for the production of bioplastics from a new biological source suing cheap raw materials. Such a process would preferably be easily adaptable as an integral part of the agricultural commercial production of bioplastics.